The present invention relates to communications systems, and more particularly, to the sectorization of cells, or coverage areas, in time division multiple access (TDMA) radio communications systems.
Most time-division multiple-access wireless communications systems employ either a time-division duplex (TDD) scheme or a frequency-division duplex (FDD) scheme to separate uplink and downlink transmissions. Since both duplex schemes provide certain advantages and disadvantages, both schemes are routinely utilized in wireless communications applications.
For example, in the Personal Wireless Telecommunication (PWT) standard, time-division multiple-access with time-division duplex is used for frequency planning as well as signal packet and time slot assignment. Such a time-division multiple-access/time-division duplex scheme is well suited for many business wireless communication applications (e.g., small-campus systems with micro or pico cells).
On the other hand, time-division multiple-access with either time-division duplex or frequency-division duplex can be preferable for licensed Personal Communication Service (PCS) frequency bands, depending upon customer demands and marketplace requirements. In other words, since the structure of a Personal Communications Service system is primarily determined by a service provider having acquired a portion of the frequency spectrum, the technology and frequency usage implemented in such a system is ultimately driven by customer demand as well as legal and practical constraints. While a first customer may request a time-division multiple access/time-division duplex system for a particular business wireless application, a second customer may thereafter demand a time-division multiple access/frequency-division duplex system for a wireless local loop application.
Thus, product and service providers are often required to convert between duplex schemes. Converting between schemes, however, typically results in duplicated effort and therefore wastes significant time and resources. For example, since the conventional time-division duplex and frequency-division duplex schemes are fundamentally different, it generally is not feasible to use a common hardware platform for both types of system. As a result, two development teams are typically assigned, and two separate product lines are usually established, to provide for both time-division duplex and frequency-division duplex implementations.
To alleviate this problem, copending U.S. patent application Ser. No. 09/189,808, entitled xe2x80x9cFlexible Frequency-Time Division Duplex in Radio Communications Systemsxe2x80x9d and filed Nov. 12, 1998, and copending U.S. patent application Ser. No. 09/189,807, entitled xe2x80x9cFixed Frequency-Time Division Duplex in Radio Communications Systemsxe2x80x9d and also filed Nov. 12, 1998, describe duplex schemes which allow a communications system to be adapted to satisfy varying customer needs without requiring modification of basic system hardware architecture. More specifically, the above cited copending applications describe mixed, or hybrid, division duplex mechanisms in which uplink and downlink transmissions can be separated in frequency while time slots associated with transmission and reception are also separated in time. The hybrid duplex schemes, referred to herein as frequency-time division duplex (FTDD), allow alternative division duplex mechanisms to be selectively implemented within a communications system without requiring modification of basic system hardware architecture. Each of the above cited copending utility applications is incorporated herein in its entirety by reference.
Advantageously, the disclosed frequency-time division duplex systems can utilize a single hardware platform for applications where either time-division duplex or frequency-division duplex is preferred. According to exemplary embodiments, the disclosed frequency-time division duplex systems are neither pure time-division duplex systems, in which the same frequency band is used for both uplink and downlink transmissions, nor pure frequency-division duplex systems in which both uplink and downlink transmissions occur simultaneously. Rather, the disclosed frequency-time division duplex systems can utilize separate frequency bands as well as separate time slots for uplink and downlink communications. Thus, a hardware platform initially designed for use in a timedivision multiple access/time-division duplex system can be readily adapted for use in a time-division multiple access/frequency-division duplex system, and vice versa, without significant hardware modification.
Furthermore, since uplink and downlink communications can be separated in both frequency and time, the disclosed frequency-time division duplex systems provide less cross-channel interference as compared to prior art systems. Also, since a single hardware path can be used for both uplink and downlink transmissions at both base stations and terminals, the disclosed frequency-time division duplex systems retain the advantages of low cost and power consumption typically associated with conventional time-division duplex systems. The disclosed frequency-time division duplex systems can also be configured to operate without loss of spectral efficiency. Further toward that end, the present invention provides methods and apparatus for providing coverage area sectorization in such frequency-time division duplex systems.
The present invention provides efficient sectorization methods for use with frequency-time division duplex communications systems. According to exemplary embodiments, a number of base stations within a communications system are strategically positioned and configured using frequency-division duplex transceivers of different time-reference type so that a duplex link can be set up anywhere within the system coverage area during any available system time slot. Advantageously, the disclosed methods provide a high degree of adjacent sector interference immunity with relatively little hardware complexity.
According to an exemplary embodiment, a base station cluster for use in a wireless communications system includes a number of base stations, each base station being configured to communicate with mobile stations in the wireless communications system and in accordance with a time division multiple access/frequency-time division duplex (TDMA/FTDD) communications format. The exemplary base station cluster includes an equal number of antennae, each antenna being coupled to a different one of the base stations and oriented such that each of the base stations communicates with mobile stations located in a sector of a coverage area serviced by the base station cluster. According to the embodiment, information signals are communicated between the base stations and mobile stations via TDMA frames, each TDMA frame including first and second time slot partitions. For example, each base station in the cluster can use the first partition of each TDMA frame exclusively for transmission of information signals to mobile stations while using the second partition of each TDMA frame exclusively for reception of information signals from mobile stations. Alternatively, a first subset of the base stations can use the first partition of each TDMA frame exclusively for transmission of information signals to mobile stations while using the second partition of each TDMA frame exclusively for reception of information signals from mobile stations, and a second subset of the base stations can use the first partition of each TDMA frame exclusively for reception of information signals from mobile stations and can use the second partition of each TDMA frame exclusively for transmission of information signals to mobile stations.
According to another exemplary embodiment, a wireless communications system having an overall coverage area with a plurality of cells includes at least one base station cluster positioned within one of the cells, each base station cluster including a number of base stations and an equal number of antennae. According to the embodiment, each base station can be configured to communicate with mobile stations in the wireless communications system and in accordance with a time division multiple access/frequency-time division duplex (TDMA/FTDD) communications format, and each antennae can be coupled to a different one of the base stations and oriented such that each of the base stations communicates with mobile stations located in a cell sector. For example, first and second base station clusters can be co-located in one cell, wherein each base station in the first base station cluster uses the first partition of each TDMA frame exclusively for transmission of information signals to mobile stations and uses the second partition of each TDMA frame exclusively for reception of information signals from mobile stations, and wherein each base station in the second base station cluster uses the first partition of each TDMA frame exclusively for reception of information signals from mobile stations and uses the second partition of each TDMA frame exclusively for transmission of information signals to mobile stations. Alternatively, a single base station cluster can be located in a cell, wherein each of a first subset of base stations in the single base station cluster uses the first partition of each TDMA frame exclusively for transmission of information signals to mobile stations and uses the second partition of each TDMA frame exclusively for reception of information signals from mobile stations, and wherein each of a second subset of base stations in the single base station cluster uses the first partition of each TDMA frame exclusively for reception of information signals from mobile stations and uses the second partition of each TDMA frame exclusively for transmission of information signals to mobile stations.
The above-described and other features and advantages of the invention are explained in detail hereinafter with reference to the illustrative examples shown in the accompanying drawings. Those of skill in the art will appreciate that the described embodiments are provided for purposes of illustration and understanding and that numerous equivalent embodiments are contemplated herein.